Machines made by the WIRTGEN Group are rehabilitating the Northern runway at Frankfurt/Main International Airport without any interruption in air traffic. The showdown takes place at night. Night after night, workers of German contractor Kirchhoff-Heine remove 900 square metres of old pavement to build a new one. For this job, VÖGELE SUPER 1900 and SUPER 2100 pavers are on the scene.

When the last aircraft has touched down and air traffic is banned until the next morning, lights go out at Frankfurt/Main International Airport. Not so, however, for the Northern runway, where hundreds of floodlights illuminate the area. Dozens of specialized workers appear at the check-in. After passing through security they head straight for the runway – they are here to work. Nobody is late when the shift starts at 10:30 at night, for time is pressing. Before the runway will be handed back to air traffic at 6:00 in the morning, the men must have shattered and removed 15 x 60 metres of runway, built a new base and paved new wearing course. They have nerves of iron, as it seems. This is the first job site of this kind in the world. It does not permit delays or downtime.

“This project is a challenge to everyone – to the workers and to us as manufacturer of the pavers and provider of services” says Dieter Schwenninger, applications expert from VÖGELE. He has been part of the team from the very beginning in order to accurately prepare the SUPER 1900 and SUPER 2100 pavers for their job and to advise the contractor on all technical issues. The contract for pavement rehabilitation was awarded to Kirchhoff-Heine Strassenbau GmbH & Co.KG based at Langenargen, Germany. No more than 9 firms had followed the invitation to tender by Fraport AG, the airport company, and submitted their bids, a circumstance not surprising in view of the complexity of the job.

“We reckon in minutes, not in hours”
Few contractors are experienced in such projects and risks are high. “Logistics are of utmost importance,” says Volker Zintel of Fraport AG. “We reckon in minutes, not in hours.” That is why Fraport AG spent a whole year preparing for the project. By summer 2005, rehabilitation of the runway will be completed after 296 overnight closures. The contract is worth 38M Euros.

For each construction machine a stand-by unit is available at all times to be on the safe side. Breakdowns or repairs on site would make it impossible to keep to the tight work schedule. For every machine its specific position is defined and for every worker his specific job. From the VÖGELE range of products, SUPER 1900 and SUPER 2100 pavers with HPC screeds in TP2 version had been chosen to do the paving job. VÖGELE engineers and the specialized workers on site prepared the pavers to perfectly match the mix to be paved. Specifications in terms of surface accuracy and truth to line and level are similar to those for road construction. The smoother the pavement, the less aircraft shudder as they touch down.

The smoother the pavement, the less aircraft shudder
The asphalt used on this project is a special mix. After thorough testing, construction experts at Frankfurt/Main International Airport decided for a high tech asphalt containing polymer modified binder. The advantage of this mix is that it can be paved at relatively low temperatures and immediately compacted by rolling. Temperature, indeed, is one of the crucial aspects on this airport project, for only little time is left for the pavement to cool. By 6 o’clock in the morning pavement temperature is low enough to bear the weight of landing aircraft. This, however, only works if weather permits. Too high ambient temperatures would prevent the mix from cooling in the short time available. As a result, paving operations are suspended during the hot summer season, during icy winter nights and also at times of heavy rainfall.

The asphalt is still steaming as the first aircraft approach
This night, too, a tracked SUPER 1900 and a SUPER 2100 paver are ready for service on the high-security job site at Frankfurt/Main International Airport. The pavers need to wait their turn. First, excavators fitted with hammers start shattering the deformed asphalt pavement with sections more than 30 years old of a runway which so far had handled some 200,000 aircraft movements a year with each aircraft weighing up to 300 tonnes. On compacted crushed stone and sand, mix for the first layer of asphalt base, 24cm thick, is then dumped, spread and compacted by dozers. Using a paver for this job is not possible due to the necessity of embedding in this layer supply piping, 22.5cm in diameter, for the light beacons alongside the runway.

After that, the second layer of asphalt base, also 24cm thick, is laid by the VÖGELE SUPER 1900 and SUPER 2100 pavers. They pave the asphalt mix at temperatures between 125 and 135°C. The pave speed is 2m/min. A wax added to the bitumen allows paving at this low temperatures. Conventional mixes need paving at temperatures a good 50°C higher.

A true challenge: high-precision work, perfectly co-ordinated, by all machines on the scene.	When the first aircraft will land in 2 hours‘ time, the pavement must have cooled by 40°C.

1,400 tonnes of asphalt paved in 4.5 hours’ time
Next is a 12cm asphalt binder course, which together with the base courses totals 60cm of special asphaltic mix. Asphalt paving needs to be carried out in 4.5 hours’ time. The density produced by the HPC screed in TP2 version is some 85% before 4 HAMM DV-8 rollers come in. Asphalt temperature still is 100°C. From that point of time 90 minutes are left for cooling by another 15°C, a temperature then low enough to allow landing with no risk neither for aircraft nor for the pavement. By the way, the workers not only pave 1,400 tonnes of special asphaltic mix for the new runway every single night, they also remove an equal quantity of debris, install light beacons for the runway and apply traffic line markings. In the morning they hand back the runway to air traffic swept perfectly clean.

Rehabilitation of the high tech runway, however, is not yet completed. So far, the individual stretches have been paved in a transverse direction. The top wearing course, however, must run parallel to the direction of take-off and landing. The reason: a pavement surface with transverse joints would cause substantial vibrations to aircraft. Therefore, every seven weeks the job site at Frankfurt/Main International Airport experiences particularly busy nights. Excavators may now disappear from the scene for five overnight closures. Instead, four WIRTGEN cold milling machines take over and start milling off 4cm of the binder course in 2m width.

Project Details: Client: Project: Duration: Completion: Contractor: Equipment: Materials: Base Course: Wearing Course: Paving Operations:

Frankfurt Airport AG Rehabilitation of Northern Runway 12 months Summer 2005 Kirchhoff-Heine Straßenbau GmbH & Co. KG, Langenargen VÖGELE SUPER 1900 and SUPER 2100 Pavers HAMM DV-8 Rollers, WIRTGEN W 2000 Cold Milling Machines Low-temperature mix with SABOBIT wax additive Pave Speed: 2m/min., Total Thickness Paved: 60cm Asphalt containing polymer modified Pave Speed: 4m/min., Layer Thickness: 4cm Laydown Rate: 1,400 tonnes in 4.5 hours, 900m2 paved, Paving Temperature: 125 – 135°C